Generally, an encoder to detect a position of a moving member is known. The encoder includes an encoder scale, which includes a scale, and a head to move relatively to the encoder scale and to read the scale of the encoder scale in the movement. As the encoder, a linear encoder to detect a position on a straight line of when a member moves in a straight line and a rotary encoder to detect a rotation angle (position) of when the member moves rotationally have been known.
Also, as a method with which the head reads the scale of the encoder scale, a magnetic method to use a magnetic head and an optical method to use an optical sensor have been known. Also, as the scale of the encoder scale, an increment method to measure a relative position and an absolute method to measure an absolute position have been known. Also, as the above-described optical method, a transmission method in which a slit is provided, as a scale, to the encoder scale and a reflection method in which a reflection surface having high reflectivity and a non-reflection surface having reflectivity lower than that of the reflection surface are included, as scale patterns having different reflectivity, in an encoder scale.
To the head in the optical method, a light emitting element and a light receiving element are provided. In the transmission-type, the light emitting element and the light receiving element are respectively arranged to both sides of the encoder scale, the encoder scale being sandwiched therebetween. On the other hand, in the reflection method, the light emitting element and the light receiving element are arranged on one side of the encoder scale. Thus, the reflection method is advantageous to downsizing compared to the transmission method.
In the encoder scale used in the reflection method, the reflection surface and the non-reflection surface having different reflectivity in respect to light emitted from the light emitting element are provided. By repetition of the reflection surface and the non-reflection surface, a scale pattern is formed. As a method for forming the scale pattern, for example, the following method has been known. That is, first, an SiO2 layer to adhere a reflection film onto a surface of a glass plate is formed. Then, an Al layer as a reflection film is formed and a Cr2O3 layer to adhere a non-reflection film to the Al layer is formed. Subsequently, a Cr layer as a non-reflection film is formed and a scale pattern is formed from a reflection surface including the Al layer and a non-reflection surface including the Cr layer by a lithography method (see, for example, Patent Literature 1).
Also, in Patent Literature 1, it has been proposed to use a metallic plate including aluminum or aluminum alloy having high reflectivity of light as a reflection-type encoder scale instead of a glass plate, to form a mirror surface on a side surface of the metallic plate by cutting processing, and to form, as a scale pattern on the mirror surface, a reflection surface having a mirror surface and high reflectivity and a non-reflection surface having reflectivity of light lower than that of the reflection surface, for example, by evaporating, to the mirror surface, chromium having reflectivity of light lower than that of aluminum.
Note that in Patent Literature 1, it has been proposed to form the non-reflection surface by decreasing reflectivity of light by performing coloring processing on the mirror surface or by performing surface-roughing processing on the mirror surface in a case of providing the non-reflection surface.
Also, as a method to form, on a plate such as a glass plate, a scale pattern including a reflection surface and a non-reflection surface, the following methods have been known. That is, for example, a method to form a mirror surface reflection part to be a reflection surface by evaporating a metallic cover film to the glass plate and by performing etching processing to a part to be the non-reflection surface on the mirror surface reflection part, and a method to form a scale pattern on a side surface of a plate to be material by performing print processing of high contrast on the plate to be a material (see, for example, Patent Literature 2).
In the above-described embodiment, for example, white is printed as a reflection surface and black is formed as a non-reflection surface on a flat-and-smooth side surface of a glass substrate, whereby a scale pattern is formed.